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IS 3548 (1988) : Code of Practice for Glazing in Buildings 
[CED 13: Building Construction Practices including 
Painting, Varnishing and Allied Finishing] 




Jawaharlal Nehru 
'Step Out From the Old to the New' 



■K^y / 1 juaaaws^fea rs^^TTF^ 



2*S< W I *>S*V2^NK^ 



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Invent a New India Using Knowledge 



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"Knowledge is such a treasure which cannot be stolen" 




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BLANK PAGE 



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PROTECTED BY COPYRIGHT 



Indian Standard 

CODE OF PRACTICE FOR 
GLAZING IN BUILDINGS 

( First Revision) 



IS -.3548- 1988 

( Reaffirmed 2005 ) 



UDC 698-3 : 00676 



© Copyright 1989 

BUREAU OF INDIAN STANDARDS 

MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG 
NEW DELHI 110002 

G* 4 May 1989 



IS I 3548 - 1988 



Indian Standard 

CODE OF PRACTICE FOR 
GLAZING IN BUILDINGS 

( First Revision J 



0. FOREWORD 



0,1 This Indian Standard (First Revision) was 
adopted by the Bureau of Indian Standards on 
19 September 1988, after the draft finalized by 
the Building Construction Practices Sectional 
Committee had been approved by the Civil Engi- 
neering Division Council. 

0.2 Glazing is an important item in building 
construction and glass has to be selected to cater 
to several requirements. The fixing of glass is 
also a specialized operation and, if not satisfac- 
torily done, will lead to the hazards of broken 
glass. With the wide adoption of glazed windows 
in industrial structures and also in multi-storeyed 
buildings, the importance of glazing and the need 
for proper workmanship has considerably increas- 
ed. This code is intended to provide guidance in 
the selection of glazing for building construction 
and also fixing operations, taking into account the 
types of sheet glass that are available in this 



country and also the exposure conditions which 
the construction will have to stand. 

0.3 This standard was first published in 1966. 
The present revision has been taken up with a 
view to updating its contents in line with the 
current practices. The important changes include 
addition of louvered glazing and new items like 
safety, wired and figured glasses, and polysulphide 
based sealants. 

0.4 For the purpose of deciding whether a parti- 
cular requirement of this standard is complied 
with, the final value, observed or calculated, 
expressing the result of a test or analysis, shall be 
rounded off in accordance with IS : 2-1960*. The 
number of significant places retained in the 
rounded off value should be the same as that of 
the specified value in this standard. 



♦Rules for rounding off numerical values ( revised ). 



1. SCOPE 

1.1 This standard covers glazing work in build- 
ings including techniques used in glazing. 

1.2 This standard does not cover fixing of glass- 
lens lights in walls or roofs, glazing in curtain 
walls, or fixing of glass facings. 

1.3 This standard does not cover puttyless or 
patent glazing. 

2. TERMINOLOGY 

2.1 For the purpose of this standard, the following 
definitions shall apply, 

2.1.1 Anchor — A strip of metal bent to an 'L' 
shape. The longer leg has countersunk holes for 
screws to fix the anchor to the background, and 
the shorter leg supports the glass without protrud- 
ing beyond the face. 

2.1.2 Back Clearance — See Clearances and Fig, 
1A. 

2.1.3 Back Putty — The portion of putty re- 
maining between the glass and the depth of the 
rebate after the glass has been pushed into posi- 
tion ( see Fig. IB). 



2.1.4 Bead or Glazing Bead — A strip of wood, 
metal or other suitable material attached to the 
rebate to retain the glass. 

2.1.5 Bedding Putty — The compound placed 
in the rebate of the opening into which the glass 
is bedded, 

2.1;6 Block — A small piece of wood, lead or 
other suitable material used between the edge of 
the glass ( generally the bottom edge only ) to 
centralize the glass in the frame ( frequently call- 
ed a setting block ). 

2.1.7 Clearances — Edge clearance and back 
clearance are as shown in Fig. 1A. 

2.1.8 Distance Piece — A small piece of wood, 
lead or other suitable material used to locate the 
glass between the bead and the back of the 
rebate, and prevent lateral movement. 

2.1.9 Expansion Tape — See Insulating Strip. 

2.1.10 Fixing Compound — A material used in 
fixing glass, applied by hand, knife or trowel, or 
as a pre-formed strip and capable of adhering to 
a wide variety of surfaces. 



1 



IS : 3548-1988 



I I 



GLAZING 
SIZE 



TIGHT SIZE 



± 



edgeJ 



-POSITION OF GLASS 
SIGHT SIZE 



N DEPTH 

^ 1_ 



R —J-— BACK 



CLEARANCE 



CLEARANCE IWIDTH ^ 

1A Glazing Rebate 



GLASS 



FRONT 
PUTTY 




STRIPPED 
AT AN 
ANGLE 



BACK 
PUTTY 




BEDDING 
PUTTY 

1B Glazing with Compound 1C Glazing into Groove 

Fig. 1 Typical Illustrations Showing 
Glazing Details 

2.1.11 Frame — See Surround. 

2.1.12 Front Putty — The compound forming 
a triangular fillet between the surface of the glass 
and the front edge of the rebate. 

2.1.13 Glazing — The securing of glass in pre- 
pared openings, such as windows, door panels, 
screens and partitions. 

2.1*13.1 Double glazing — A form of glazing 
which incorporates, instead of a single pane of 
glass, two panes separated by substantially sta- 
tionary air, for the purpose of sound or thermal 
insulation or both. It may consist of: 

a) two separate window frames, each single- 
glazed fixed in the same wall opening; 

b) one window frame carrying two sashes 
coupled together, each separately glazed; 

c) one window frame carrying two separate 
glasses, usually glazed on site; 

d) one window frame single-glazed, with a 
second glass attached by clips or other 
means; and 

e) one window frame carrying a factory-made 
hermetically-sealed double glazing unit. 

Note — Patent glazing systems designed for 
double glazing are covered in IS : 104-39-1983*. 



♦Code of practice for patent glazing. 



2.1.13.2 External glazing — Glazing, either 
side of which is exposed outside the building 
( contrast with outside glazing ). 

2.1.13.3 Louvered glazing ( horizontal ) — A 
glazing with strips of glasses placed angular and 
one above the other at a distance sloping outside. 

2.1.13.4 Louvered glazing ( vertical ) — A 
glazing with strips of glasses spaced vertically 
side by side at an angle. 

2.1.13.5 Multiple glazing — A form of glaz- 
ing based on the same principle as double glazing, 
but incorporating three or more panes of -glass. 

2.1.14 Glazing Compound — A material used in 
glazing, applied by hand, gun, knife or trowel, to 
provide a bedding for the glass and weather-tight 
joint between glass and surround. 

2.1.15 Inside Glazing — External glazing in 
which the glass is inserted from inside the build- 
ing. 

2.1.16 Outside Glazing — External glazing in 
which the glass is inserted from outside the build- 
ing. 

2.1.16.1 Outside face — Keeping of the rough 
surface of textured or other glass outside while 
fixing the glass. 

2.1.17 Internal Glazing — Glazing, neither side 
of which is exposed outside the building ( contrast 
with inside glazing ). 

2.1.18 Insulating Strip — A strip of resilient 
material used to insulate the edge of the glass 
against rigid contact with non-resilient material 
( sometimes called expansion tape ) . 

2.1.19 Pane — A piece of glass cut to size and 
shape ready for glazing ( often called a square ). 

2.1.19.1 Louvered pane — A strip glass cut to 
the size of louver with smoothened edges ready 
for fixing. 

2.1.20 Peg — A small metal component used 
in glazing to hold the glass in a metal frame 
( sometimes called spring ). 

2.1.21 Pointing Compound — A plastic non- 
setting compound having a workable consistency 
so that it may be handled and filled into joints 
readily. 

2.1.22 Rebate — The part of a surround; the 
cross-section of which forms an angle into which 
the edge of the glass is received. 

2.1.23 Saddle Bar — A metal stiffening bar 
across the face of the glass and secured to the 
surround, to which a leaded light is tied. 

2.1.24 Sash — See Surround. 

2.1.25 Sealer — A liquid compound of brushing 
consistency applied to a surface to prevent the 
absorption of soils from the glazing or fixing 



IS : 3548 - 1988 



compounds, or to prevent attack by alkalis on 
these oils. 

2.1.26 Setting Block — See Block. 

2.1.27 Sizes 

a) Daylight size ... ( sight size ) 

b) Full size ... ( tight size ) 

c) Glass size ... ( glazing size ) 

2.1.27.1 Sight size ( daylight size ) — The 
actual size of the opening which admits light 
( see Fig. 1A ). 

2.1.27.2 Tight size {full size } rebate size ) — 
The actual size of the rebate opening ( see Fig. 
1A ) ( contrast with glazing size ). 

2.1.27.3 Glazing size (glass size) — The 
actual size of a piece of glass cut for glazing 
( see Fig. 1A ). 

2.1.28 Spring — A small headless nail or trian- 
gular piece of metal used, in addition to putty, 
for securing panes of glass in surrounds ( see also 
Peg). 

2.1.29 Spring Clip — A small metal component 
used, in addition to putty, for securing panes of 
glass in metal frames. 

2.1.30 Square — See Pane. 

2.1.31 Surround — Any frame, sash, casement 
or other building component into which glass is 
glazed. 

3. NECESSARY INFORMATION 

3.1 The following necessary information for effici- 
ent planning and distribution of the work shall be 
furnished by the general building contractor: 

a) Type of glass to be used with details, such 
as colour, pattern and ornamentation; and 

b) Details of the techniques to be employed 
in the work and other materials to be 
used. 

3.2 The following information shall be given to 
the supplier when glass is ordered: 

a) Type, quality thickness and substance of 
glass; 

b) In specifying sizes, the first dimension given 
should be the height. Mode of measure- 
ments taken, that is, tight size, glass pane, 
size, etc, shall be mentioned. In case of 
extra allowance required for coloured glass, 
tight size with allowance required shall be 
indicated; 

c) In specifying sizes of preparing templates 
for shaped glasses, the face side should be 
specified; 

d) In specifying sizes for bevelled plates, 
decorated plates, factorymade double glaz- 
ing units, leaded lights, copper lights or 
louvre ventilators, both tight and sight 
sizes should be given; 



e) In all cases where patterned glass, decorat- 
ed glass, leaded lights or copper lights are 
required to align, this should be specified 
and a dimensional sketch provided, if 
necessary; 

f ) In cases where wired glass is required to 
align one way between adjacent paries 
within the limits of manufacture, this 
should be specified; and 

g) When ordering bent glass, the following 
additional items should be provided: 

1 ) Bent one way only to curve or series of curves 
— A rigid template cut to the exact 
curve and marked to indicate whether 
it represents the concave ( hollow ) or 
convex ( round ) side of the glass; 

2) Bent one way of the pane only, the curve 
being arc of a circle — A drawing show- 
ing straight edge, girth and radius of 
curve may be acceptable to the vendor 
in place of a template, provided it is 
marked to indicate whether it represents 
the concave ( hollow ) or the convex 
( round ) side of the glass; and 

3) Bent both ways of the pane 9 whether the 
curves are simple curves or not — A rigid 
body mould shaped to the exact contour 
of the pane and marked to indicate 
which side of the glass it represents. 

4. MATERIALS 

4.1 Glass used for glazing in buildings should 
conform to following Indian Standards: 

a) Sheet glass — IS : 2835-1977* 

b) Safety glass — IS : 2553-1971f 

c) Wired and figured — IS : 5437-1969J 
glass 

4.2 Glazing compound for glazing should conform 
to following Indian Standards: 



a) Putty 

b) Polysulphide based 
sealants 



— IS : 419-1967§ 

— IS : 11433 
( Part 1 )-1985|j 

IS : 12118 
(Part 1 )-1987^J 

Note 1 — Compounds for Glazing in Concrete, Stone, 
Brick or Asbestos cement — These types of compound nor- 
mally need to be sealed to prevent absorption of oil 
from the glazing compound, unless the compound has 
been specially formulated; resistance to alkali is gene- 
rally important. A non-setting compound may be used, 
provided it is painted. 



♦Flat transparent sheet glass ( second revision ). 

fSafety glass ( second revision ). 

JWired and figured glass. 

§Putty for use on window frames {first revision ). 

[[Specification for one part gun-grade polysulphide- 
based joint sealants: Part 1 General requirements. 

^Specification for two parts polysulphide based sealant: 
Part 1 General requirements. 



IS : 3548 - 1988 



Note 2 — Non-setting Compounds — These are needed 
for use with colour and heat-absorbing glasses which 
will become hot in sunshine and which are, therefore, 
liable to expand and contract much more than ordi- 
nary glass. The fact that non-setting compounds are 
easily finger marked make it undesirable to use them 
without beads, except in relitively inaccessible situa- 
tions. If, in order to prolong its life, or for other 
reasons, the compound is required to take paint, refe- 
rence should be made to the manufacturer of the 
compound. 

5. DESIGN 

5.1 Selection of Thickness of Glass — For 

vertical windows secured on four edges, the 
minimum thickness of glass shall be found as 
follows: 

a) The maximum wind load average over a 
one-minute period or preferably 3-second 
period should be ascertained ( see Note ). 

b) Allowance should be made for both inward 
and outward pressure and the maximum 
pressure as a result of combination of this 



fact shall be found; correction for relevant 
height of the building and also for shield- 
effect of obstructions sorrounding the 
buildings should be made in accordance 
with the principles laid down in IS : 875- 
1964*. 

c) The glass factor for the particular use 
should be found by dividing the area of the 
glass pane expressed in m 2 by the peri- 
meter in running metres. 

For rectangular area, for instance, this 
A x B 



would be - 



where A and B 



2{A+B) 
are the dimensions of the sides in metres. 

d) The minimum thickness of glass corres- 
ponding to various wind loads shall be 
found from Fig, 2, knowing the design 
pressure and glass factor. 



♦Code of practice for structural safety of buildings: 
Loading standards ( revised ). 



500 



LENGTH OF SHORTER SIDE (mm) 
1000 1500 2000 2500 



3000 




2000 

1750 

1500 
1250 

1000 
750 

500 



250 

PLATE SHEET WIND 

THICKNESS PRESSURE 
(mm) ( N/m 2 ) 



♦Weight of gla?s in kg/m a approximately equal to 2*6 times the thickness in millimetres. Nomogram for determining 
thickness of window panes for various wind pressures. ( Modulus of rupture of sheet glass taken as 38 N/mm 8 and of 
plate glass as 19 N/mm2 after making allowance for variability of strength )«. 

Fig, 2 Nomogram for Determining Thickness of Glass Plate and Sheet 

for Window Panes 



IS : 3548 - 1988 



Note — Wind load data collected over a long 
period will be available from the Meteorological 
Department and from this the maximum wind 
velocity and pressure corresponding to specific 
duration may be found. Unless very severe condi- 
tions of exposure warrant special considerations for 
design, the wind pressure data recommended in 
IS : 875-1964* ( which correspond to measure- 
ment taken over a period of about 5 minutes ) may 
be used in normal circumstances. 

5.2 Durability — Though, under ordinary con- 
dition, glass has excellent durability, all glasses 
•are subject to deterioration by action of water 
and prolonged attack by alkaline solutions may 
damage glass. If glass is allowed to remain dirty 
for a long period, the dirt film will tend to hold 
Avater and in this way, a process of surface attack 
may begin. 

53 Fire Resistance — In regard to fire resist- 
ance requirements for glazing, reference may be 
made to IS : 1642-1 960 1. 

5.4 Thermal Expansion and Contraction — 

For heat absorbing glass and clear glass with 
painted surface especially where the colour is 
black and when ordinary glass is used under dark 
background, the following special protections are 
necessary to provide for thermal expansion and 
contraction, and temperature of the glass may be 
liable to large variations on exposure to sunshine: 

a) Where the longer dimension is less than 
750 mm, a glazing allowance of not less 
than 3 mm shall be given. Where the 
longer dimensions exceeds 750 mm, not 
less than 5 mm clearance all round shall be 
given; 

b) The minimum cover necessary for safe 
glazing, except where toughened glass is 
used, shall not exceed 10 mm as otherwise 
there is risk of cracking owing to the 
shielded edge remaining colder than the 
exposed area; and 

c) Glazing compound should be non-setting 
compound and all absorbent rebates and 
grooves should be treated with a sealer and 
not merely primed. 

5*5 Light Transmission and Heat Insula- 
tion — For improved heat and sound insulation, 
•double or multiple glazing may be used. The heat 
insulation depends upon spacing and scarcely at 
all on the thickness of the glass used. For vertical 
glazing, the insulating value increases up to a 
spacing of about 10 mm, beyond which there is 
little further change. However, the spacing of as 
little as 3 mm will provide an insulating value of 
50 percent of this maximum. For inclined or 
horizontal glazing, there may be some advantages 
in using a spacing greater than 20 mm where this 
is practicable. However, while designing for heat 

*Code of practice for structural safety of buildings: 
Loading standards ( revised ). 

fCode of practice for fire safety of buildings ( general ): 
Materials and details of construction. 



insulation, it should be remembered that frame 
members of high thermal conductivity may 
provide direct paths for heat leakage between the 
inside and outside air and thus appreciably impair 
the insulating value of the installation as a whole. 
The values of different light transmittence and 
heat/light ratio is given in Table 1. 



TABLE 1 DIFFUSE LIGHT TRANSMITTANCE AND 
HEAT /LIGHT RATIO OF GLAZING MATERIALS 

Materrial Thickness Diffuse Heat/ 

mm Light Trans- Light 

mittanoe Ratio 



Clear glass 


3*0 


0-85 


0*86 


Double glazing 
( clear glass ) 


3*0 each 


0*72 


0-74* 


Heat absorbing 
glass 


3-2-3'5 


0*62 


0*24 


Figured glass 


3-2 


0*78 


0*83 


Wire-cast glass 


6*0 


0*67 


0*71 



♦Double glazing reduces heat/light ratio. Further, the 
heat insulation of double glazing also improves due to air 
gap causing reduction of the overall heat transmission 
coefficient. 



5.6 Sound Insulation — For sound insulation, 
reference may be made to IS : 1950-1962*. For 
effective sound insulation, spacing of the order of 
100 mm and above be adopted in case of double 
or multiple glazing. Thicker glass also provides 
insulation. Further improvements may be effected 
by lining the surrounds between the glasses with 
a sound absorbing material. 

5.7 Rebates and Grooves — These should be 
rigid and true. Rebates for normal glazing shall 
be at least 8 mm deep, for small panes rebate may 
be 6 mm deep. For large windows, such as shop 
windows, the frame rebates at the tops and sides 
should be at least 10 mm and at the bottom 
12 mm. Rebates for double or multiple glazed 
sealed units shall be 16 mm deep generally, unless 
otherwise advised by the manufacturers of the 
particular units. Rebates for flat glass without 
beads should be wide enough to accommodate the 
back putty, the glass and the front putty stripped 
at an angle. A wider rebate is needed for bent 
glass than for flat glass. For glazing with beads, 
rebates should be wide enough to accommodate 
glass and beads and to allow a minimum clea- 
rance of 1*5 mm at both the back and front of the 
glass. Rebate and grooves shall be clean and 
unobstructed before glazing. 



♦Code of practice for sound insulation of non-industrial 
buildmgs. 



IS : 3548 - 1988 



6. GLAZING 

6*1 Size for Glass — The size of glass for glaz- 
ing shall allow a clearance between the edge of 
glass and surround as specified below: 

For wood or metal surrounds 2*5 mm 
For stone concrete or brick 3*0 mm 

The clearance may be increased, provided the 
depth of the rebate or groove is sufficient to 
provide not less than 1*5 mm cover to the glass, 

6.2 Location of Glass in Frame — The glass 
shall rest upon two blocks to locate the pane 
properly within the surround. In the case of small 
panes, use of blocks may not be necessary. When 
glazing in side-hung windows or doors, the glass 
shall be located by blocks so that it bears on the 
bottom of the surround at a point near the hinge, 
but is not brought into contact with the surround 
and does not suffer undue stress. 

6.2.1 When glazing in horizontal centre-hung 
sashes, which may be turned through about 180°, 
additional blocks shall be placed between the top 
edge of the glass and the surround to prevent 
movement of the glass when the sash is inverted. 
Where the panes are more than 90 mm high, the 
glass shall be located at the two pivoting points 
by blocks of suitably resilient material, such as 
chloroprene. 

6.3 Preparation of Rebates and Grooves in 
Wood — Rebates or grooves should be primed 
to prevent excessive absorption of oil from the 
putty. If a shellac varnish or gloss paint is used 
for this purpose, the wood may be completely 
sealed and setting of the putty unduly delayed. 

6.3.1 Absorbent hardwood frames that are not 
to be painted should either be primed with a 
medium composed of equal parts of exterior 
varnish and white spirit, and glazed with linseed 
oil putty or be completely sealed with a coat of 
unthinned exterior quality varnish and glazed 
with metal casement putty ( which will need to 
be painted ), or with a non-setting compound. 
Where hardwoods such as teak which are comple- 
tely non-absorbent are recommended metal 
casement putty should be used. If the wooden 
frame has been treated with a preservative, 
according to the instructions of the manufacturer 
of the glazing compound, preparation of rebates 
and grooves should be made. 

6.3.2 In the case of stone, concrete, brick or 
other similar materials, the rebates of grooves 
should be sealed with an alkali-resisting sealer and 
allowed to dry before glazing. The compound 
shall be metal-casement putty. 

6.4 Glazing with Compound — This method 
is suitable for window and door panes where the 
combined height and width do not exceed the 
maximum shown in Fig. 1 for appropriate 
exposure grading. 



6.5 Glazing with Beads — This method should 
be used for window and door panes where the 
combined height and width exceed the maximum 
shown in Fig. 1 for glazing in unpainted hard- 
wood frames and framed shopfronts for double 
and multiple glazing units as defined in 6.9 (d), 
and wherever a non-setting compound is used in 
a position where it is liable to be disturbed. 

6.6 Glazing with Compound into Rebates — 

Sufficient compound should be applied to the 
rebate so that, when the glass has been pressed 
into the rebate, a bed of compound ( known as 
back putty ) not less than 1*5 mm thick will 
remain between the glass and the rebate; there 
should also be surplus of compound squeezed out 
above the rebate which should be stripped at an 
angle ( see Fig. IB ) not undercut, to prevent 
water accumulating. The glass should be secured 
by springs or spring clips spaced not more than 
450 mm apart measured around the perimeter of 
the pane, and afterwards fronted with compound 
to form a triangular fillet stopping 1"5 mm short 
of the sight line so that the edge of the com- 
pound may be sealed against the glass by paint- 
ing, without encroaching over the sight line. 

6.7 Glazing with Compound into Grooves — 

The glass should be pressed into glazing com- 
pounds previously placed in the groove. The 
spaces between the glass and the sides of the 
groove should be filled with compound, which 
should then be stripped at an angle ( see Fig. 1G ) 
not undercut. 

6.8 Glazing with Beads Alongwith Com- 
pound — Sufficient compound should be applied 
to the rebate so that when the glass has been 
pressed into the rebate, a bed of compound 
( known as back putty ) not less thad 1*5 mm 
thick will remain between the glass and the 
rebate. There should also be a surplus of com- 
pound squeezed out above the rebate which 
should be stripped at an angle not undercut, to 
prevent water accumulating. Bead s should be 
bedded with compound against the glass and 
wood beads should also be bedded against the 
rebate. 

6.8.1 Care should be taken to ensure that no 
voids are left between the glass and the bead. For 
outside glazing, hollow beads are undesirable 
unless they can be completely filled. 

6*8*2 With non-setting compound and where 
there is a risk of glazing compound being dislod- 
ged by pressure, front and back-distance pieces 
( to maintain face clearances ) should be used. 
Distance pieces should be completely embedded 
in the compound. 

6.8.3 Beads should be secured to wooden 
frames with either panel pins or screws and to 
metal frames in the way provided for in the frame. 
In securing to wooden frames, an adequate 



IS : 3548 - 1988 



number of fixing for the beads should be used so 
as to prevent flexing or movement of the beads. 

6.8.4 The external glazing should be as far as 
possible fixed from outside with beads as stated 
in 6.8. 

6.8.5 Where it is not possible to fix the class 
from outside, especially in a multistoreyed 
building, it may be fixed from inside with sealing 
compound as shown in Fig. 3. 



TOP BEAD 



SIDE BEAD 



INSIDE 




-SHUTTER 
CLEARANCE 



OUTSIDE 



BEAD 



CLEARANCE 



■SEALING 

SECTION A A 

-BEADING A 



COMPOUND 



OUTSIDE 




INSIDE 



*Can be fixed prior to or after placing the glass pane as 
per site conditions. 

Fig. 3 Inside Glazing 

6.8.6 Figured glasses are used to avoid direct 
sunrays and to get diffused light. This can be 
achieved advantageously by placing rough surface 
of the glass facing outside. As the surface of glass 
from inside is smooth, it will facilitate in pasting 
of colour plastic film on inside surface, whenever 
required. In that case, it will be difficult to clean 
the rough surface of glass which is outside but it 
can be cleaned by a water jet. 
6.9 Double and Multiple Glazing — The pro- 
blems connected with the application of double 
and multiple glazing are briefly as follows: 

a) Two Separate Window Frames, Each Single- 
glazed — These are preferable for sound 
insulation. To avoid problems of dirt and 
moisture in the air space s means of access 
to the cavity should be provided. 

b) One Window Frame Carrying Two Sashes 
Coupled Together, Each Separately Glazed — 
The glazing may be in separate rebates, 



one inside-glazed and the other outside- 
glazed, or in single, wide rebates with 
spacing beads. The former methods has 
the advantage that either pane can be 
replaced without disturbing the other. 
However, carefully such glazing is done, 
it may be necessary to open the cavity at 
frequent intervals for the purpose of clean- 
ing. 

c) One Window Frame of Sash Single-glazed Pro- 
vide d with Clip to Permit the Attachment of a 
Second Glass — This system involves no 
serious cleaning problems since the clipped- 
on panes can be quickly detached. Their 
main use is on existing windows which 
cannot otherwise be modified. 

d) Double or Multiple Factory-made Hermetically 
Sealed Units — Problems of cleaning of 
inner surfaces does not arise. Adequate 
rebate shall be provided in accordance with 
manufacturer's instruction. 

6.10 Double Glazing Other than Factory- 
made Sealed Units — To minimize entry of 
warm moist air from the interior of the building 
or penetration of rain from outside into the cavity, 
the glazing should be done in a careful and tho- 
rough manner. Where opening sashes are provi- 
ded, it is essential that they should fit closely. A 
small breathing hole or tube should be provided 
from the bottom of the cavity to the outside to 
ensure that such breathing vents are kept clear of 
paint or other obstructions. 

6*10.1 Where separate panes are glazed in one 
sash, it is preferable to use preformed strip of 
compound for the back putty in glazing the 
second pane, in order to provide full back putty 
with a neat finish. Usually it is better to glaze the 
outer pane first. 

6.11 Factory-made Double or Multiple Seal- 
ed Units — When ordering factory-made double 
or multiple sealed units, the following points may 
be taken into account: 

a) Both tight size and sight size ( not glazing 
size ) should be specified; 

b) Sealed units should be checked in the open- 
ing for edge clearance consistent with the 
manufacturer's recommendations. It is 
essential to follow any recommendations 
given by the manufacturer concerning the 
correct edge to be glazed at the bottom. 
Units should be positioned in the com- 
pound approximately one quarter of the 
total length from each end. The width of 
the blocks should be not less than the 
thickness of the sealed units and their 
thickness should be such as to position the 
units centrally in the opening. This thick- 
ness of glazing compound between the glass 
and the back of the rebate, and between 



IS : 3548 - 1988 



c) 



d) 



the glass and the bead should be about 1 6,13 Maintenance 

mm; 

Special techniques of glazing are required 
to protect the seal and reference should be 
made to the manufacturer of the glazing 
units; 



A non-setting glazing compound having 
good adhesion to glass and frame should be 
used. All absorbent rebates and beads 
should be treated with a sealer ( priming 
is not sufficient ); 

e) Glazing with beads should always be used. 
Hollow beads are not recommended; and 

f ) Where there is a risk of the glazing being 
dislodged by pressure, front and back 
distance pieces should be used to maintain 
face clearance. 

6.12 Louvered Glazing — This type of fixed 
glass louvers are recommended for toilets, stores, 
etc, where permanent ventilation is required. 

6.12.1 Louvered Glazing ( Horizontal ) — Glass 
strips with rounded edges are inserted from inside 
in the grooves placed one above the other. The 
grooves shall be angular preferably at 45° on the 
frame. The grooves shall overlap over each other 
by at least 20 mm as shown in Fig. 4. 



FRAME 



20mm 



BEADING 



GLASS 
STRIP 



INSIDE 




GROOVE 



20 mm 



OUTSIDE 



Note — The depth of groove may be thrice the 
thickness of glass and width of the groove may be 1 to 
1*5 mm more than the maximum thickness of glass. 

Fig. 4 Fixed Glazed Louvered Window 

6.12.2 Louvered Glazing {Vertical) — Glass strips 
are placed angularly and vertically, and inserted 
as described in 6.12*1. 



6.13.1 Cleaning — Glass should be cleaned regu- 
larly. Failure to do this will result in considerable 
reduction of daylight indoors, and may also result 
in discolouration and deterioration of the surface. 
Warm water with soap or a mild domestic deter- 
gent, followed by a clean water rinse is generally 
adequate for routine cleaning. For transparent 
glasses, cloth or wash leather should be used; for 
glasses with a broken or textured surface, a stiff 
plastic or bristle brush will be found effective. 
Where the above methods fail to remove obsti- 
nate dirt from transparent glass, polishing with 
whiting in water or methylate spirits may be 
found to be successful. Corrosive cleaning liquids 
are also sometimes employed, but should be 
handled with great care and should be sluiced 
away with excess of clean water as soon as 
possible after use to avoid damage to glazing or 
fixing compounds, window frames or any other 
materials near to the glass. Organic solvents are 
also useful for special purposes, for example, 
petrol or benzene for removing tar, turpentine 
for paint that has not dried hard and paraffin for 
grease. The solvents should, however, be carefully 
cleaned off the glass afterwards and, in some 
instances, the fire risk may need to be guarded 
against during use. Plaster or mortar splashed on 
the glass may be removed with a thin razor blade 
preferably before the material has set hard. Dried 
paint may be removed similarly. In using the 
razor blade, excessive force should not be used. 

6.13*1.1 If a trial shows that none of the 
above methods is likely to be quickly successful, 
it may be more economical to replace the glass. 

6.13.1.2 Where the cleaning of embossed,. 
sand blasted or decorated glasses has been neglec- 
ted, ordinary window cleaning methods may not 
be expected to be successful and treatment by a 
specialist is required. 

6.13.2 Replacement — If wired glass is broken 
and allowed to remain exposed to weather con- 
ditions, moisture will penetrate to the wire which 
will rust. This will result in failure of the wire, 
which may allow the glass to fall. It is, therefore, 
essential that any breakage be made waterproof 
at once with a material such as a bituminous 
paint and replacement undertaken with new glass 
as soon as is practical. 

6.13.3 Maintenance of Glazing — Glazing com- 
pound shall be regularly painted except where 
special materials are used. The building main- 
tenance shall ensure that the metal work surro- 
unding the frame do not corrode resulting in 
closing of gaps between the frame and glass or 
warping of timber with consequent breakage of 
glass.